Korean Patent Application Nos. 2000-63790 and 2000-42128, International Application No. PCT/KR00/01530 and its International Publication No. WO 02/11791 A1, all of which are incorporated herein by reference in their entirety, disclose a portable liquid supply apparatus for continuously injecting medicine into a patient in a constant quantity per unit time and over a long period of time for the purpose of curing of a specific disease. In order to continuously inject a medicine in a constant quantity per unit time and over a long period of time, the patient should be in a hospital or stay at home. This is economically and physically inconvenient for the patient and his/her family. Therefore, the aforementioned patent applications disclose an improved portable liquid supply apparatus capable of injecting the medicine in a constant rate in order to eliminate such inconvenience and cure the patient over a long period of time.
In such a liquid supply apparatus, it is important to continuously inject the medicine in a constant quantity per unit time for a predetermined period of time. The liquid supply apparatuses disclosed and proposed in the patent applications are apparatuses for injecting medicine at a constant rate, wherein a piston is pushed by means of mechanical drive or by an action of gas produced at a constant rate.
A device for pushing the piston by the production of gas is a device constructed to cause solid and liquid materials, which are separately stored, to come into contact and react with each other so that the gas is produced therefrom. Particularly, the solid material consists of sodium bicarbonate (NaHCO3) and KBr; or sodium bicarbonate, gelatin and a small amount of Talc. The liquid material consists of an L-tartaric acid (C4H6O6) solution. They are caused to react with each other to produce CO2 gas of which produced gas pressure in turn pushes the piston.
However, it is not easy to consistently maintain an initial amount of gas, i.e. CO2 gas produced by means of the reaction between the solid and liquid materials, and to consistently control and maintain a production rate of the gas thereafter, which are disclosed in the patent applications.